Abstract

On 27 January 2010 a small eruption of basaltic lava occurred 75 km NE of Quetta, Pakistan. This was highly unusual – no eruptions from this magmatically inactive area have ever been reported. Two petrographically distinct basalts types were indentified in the vesicular eruptive products. One basalt type consists of completely fresh, light brown glass with a few (<1 vol.%) partially resorbed quartz-rich xenoliths, whereas the other type is non-glassy and the lava is completely devitrified. These types also have slightly different geochemical signatures that can be partially explained by crustal assimilation. Re-melting of local basaltic rocks by short circuiting of a ruptured high-tension electrical cable is considered unlikely. Mantle melt modelling suggests that the lavas have been largely derived from a source in the garnet-spinel transition zone, i.e. well within the lithosphere. It is proposed that localized asthenospheric melting resulted in relatively depleted melts which were substantially contaminated by fusible lithospheric mantle en route to the surface. Further small-scale eruptions cannot be ruled out.

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